The present invention relates to a synchronization recovery circuit for an incoherent xcfx80/4 QPSK modulator (four-state phase modulation with a jump of xcfx80/4) intended for a personal mobile telephone system.
The PHS mobile telephone system currently used in Japan is a time division multiple access/time division duplex (TDMA/TDD) system. Reference may be made to xe2x80x9cpersonal handy phone systemxe2x80x9d RCR standard, version 1, RCR STD-28 published on Dec. 20, 1993.
It uses a DQPSK modulation scheme with a shift of xcfx80/4 at 192 K bauds/s.
Differential detection is used in systems of this type because of low complexity and moderate power consumption requirements
In the case of channels where there is Rayleigh fading, differential detection has lower error rate. Reference may be made to the article xe2x80x9cModems for Emerging Digital Cellular-Mobile Radio Systemsxe2x80x9d, IEEE Trans Veh. Tech, volume 40, No. 2, May 1991. In order to achieve a further reduction in the complexity of the receiver, and therefore its power consumption, the received signal is usually demodulated at an intermediate frequency (IF).
The IF signal is discretized, the positive values of the signal being translated into a high level, whereas the negative values are translated into a low level, and differential detection is carried out by using this discretized signal.
Given that the information is contained in the phase of the signal, which does not vary on account of the discretization, this signal can be used for phase detection.
A general object of the invention is to improve the recovery of the synchronization of the signal reaching a mobile-telephone receiver.
Given that the information is contained in the phase of the signal, which does not vary on account of the discretization, this signal can be used for phase detection.
A general object of the invention is to improve the recovery of the synchronization of the signal reaching a mobile-telephone receiver.
It therefore relates to a method for recovering synchronization on a signal transmitted to a mobile telephone receiver, characterized in that it consists in:
detecting the synchronization packet contained in the transmitted signal,
acquiring a clock phase in a coarse acquisition mode, during which the synchronization is acquired to within one quarter of the duration of a symbol,
refining this estimate in a fine acquisition mode, which is a first-order phase-locked loop operation ensuring rapid synchronization acquisition with small final fluctuation.